Two-way telephone system



B. A. TREvoR ETAL TWOJIAY TELEPHONE SYSTEM Filed oqt. so, 1943 Aug.. 12, 1947.

Patented Aug. 12, 1947 TWO-WAY TELEPHONE SYSTEM Bertram A. Trevor and John B. Atwood, Riverhead, N. Y., assgnors to Radio Corporation of America, a corporation of Delaware Application October 30, 1943, Serial No. 508,354

11 Claims.

This invention relates to circuit arrangements for two-Way telephone systems. A fundamental feature of the invention resides in the relay circuit arrangements for facilitating the conditioning of apparatus so that i-t will normally be held in a standby condition awaiting an outside call, and at other times, by means of a push button on a handset, the apparatus may be suitably conditioned for transmitting a message. In the standby condition no anode voltage is supplied to the transmitter, and hence there is no radiation therefrom.

It is an object of our invention to provide a novel circuit arrangement for a two-way radio telephone system.

It is a more specic object of our invention to provide relay-operated circuits whereby Ythe necessary transfer of controls from receiver to transmitter and vice-versa is made possible by the actuation of a push button mounted on the telephone handset.

Other objects and advantages of our invention will become apparent in the following detailed description which is accompanied lby a drawing, the sole figure of which represents a preferred embodiment.

Referring to the drawing, We show a handset 25 in which are included a microphone l, an earphone 2, and a push button 3 for closing circuit contacts 26. The handset 25 is associated with a so-called call box which may be located at any suitable point more or less remote from the receiving and transmitting units 22 and 24 respectively. Another handset (not shown) may also be plugged into the circuit by means of two jacks 20a and 2Gb. In such a handset the microphone circuit would include a plug for insertion in the jack 20a., and the earphone would be plugged into the jack 2Gb. We preferably use a conventional double plug, the plug shanks being suitably spaced apart to fit into adjacent jacks.

The receiver 22 is maintained in a standby condition by means of a power supply 23. An independent power supply 9 is associated with the transmitter 2li.,V Certain sections of this transmitter power supply are also maintained operative during standby conditions as well as during conversation. Thus the transmitter tube laments may be continuously heated, if desired, and direct current may be obtained by rectification of a 60-cycle source, for use in biasing the tubes, and also for relay operation. Another section of the power supply 9 comprises 'a transformer 3l the primary of which is normally open-circuited and the secondary of which is connected 5 for energizing ythe same.

to a rectifier circuit for producing the anode voltage. Relay 'l has a contact d in circuit with the primary of transformer 3|, so as to provide control of the transmitter output in dependence upon the pressing of the push button 3 on the handset. The push-button-to-relay circuit will presently be traced.

Three relays 4, 5, l, and an antenna relay having coils 8 and l) are preferably used. Their function will be described in the ensuing paragraphs covering the mode of operation.

An alarm system which may include a bell 30 is arranged to be actuated in response to the receipt of an incoming carrier wave. This carrier wave may be amplified and rectified by means not shown, but the derivative is preferably a direct current which is applied to the relay When relay 5 operates, it closes a circuit (to be more completely traced hereinafter) through relay 4 which operates an alarm circuit, the latter being either audible or visual. The alarm is here shown as a bell. Switch 2l is normally closed when the station is held in a standby condition but can be automatically opened during a telephone conversation in order to silence the alarm. Automatic operation is provided, as is conventional, by mounting the switch 2l in a cradle for the handset so that circuit closure depends upon the weight of the handset when resting on a push button.

Various other pieces of apparatus are also in.- cluded in the system, an illustrative embodiment of which is herein shown. The coordination of functions of the several units Will, however, be best understood by a full description of the mode of operation.

The handset and associated equipment comprised in a so-called call xbox may be located at a remote point with respect to the transmitter and receiver. The call box has associated with it a handset 25 consisting of Ithe microphone I, receiver 2, and push button 3. It also has a relay 4 which closes when a carrier is present in the receiver and operates an alarm circuit which may be a light, bell, or other indicator The circuits are drawn with the equipment in the receiving condition, but with no carrier being received. In this condition, the carrier-operated relay 5 short-circuits one half of the audio output transformer 6 of the receiver and acts as a partial squelch. This prevents excessive noise in the handset receiver when no signal is present. The handset receiver 2 is connected to the output transformer 6 through contacts aand b of buzzers.

relay i. The antenna circuit relay is held in the receiving position as shown by current from the negative section of the transmitter power supply 9 owing through contacts c of relay 1, through the relay winding ill, and thence through resistors H and l2 to ground. The resistors vIl and I2 limit the current to` a suitable value.

When the station is called from a remote point the incoming carrier wave is amplified and rectied. A rectification component causes relay to be operated. This removes the short circuit from the audio output transformer E and applies a push-push voltage to the line from the receiver power supply 23 through current limiting resistor 1 i3. Current flows through contacts a and'b(` of relay through the center-tapped choke I4, through the relay 4 to ground and back through ground to the receiver power supply. This cur'- rent operates relay 4 for the purpose of actuating an alarm circuit. When the calling station shuts off its transmitter, these circuits return to the standby position.

To answer a call, the handset is lifted from its cradle, thus silencing the alarm. Then the microphone switch 3 on the handset is closed. The input transformer l5 has two primary windings and one secondary winding. Closurerof the microphone switch 3 causes'current to flow as follows: From the transmitter power Asupply to ground, through one primary winding of transformer l5 'which is grounded, through switch 3,

' microphone l, the other primaryV winding of transformer I5, the relay coil l, resistor Il, relay winding I0, and contact c of relay 'l to the negative terminal of the power supply 9.

This causes relay 1 to operate, which disconnects the handset receiver 2 from the audio output transformer and connects it across thev microphone circuit through blocking condensers` I6 and resistors I'l. This is to supply sidetone, the resistors'l'l being provided as means for setting the sidetone level.

Relay 'i also closes circuits through its contacts c andd for placing the transmitter in opi eration. The resistor-condensercombinations 2l, Y28 are merely spark Suppressors on the relay con-Y tacts. Contact c feeds current through the antenna relay coil 8, thus connecting the antenna tothe 'transmitter 24. While contacts of lrelayl j are moving, Vthere is a momentary opening of the D. C.Y circuit which would cause the Ycircuits to return to the 'receivingpositio-n, 'where the4 circuit wouldbe closed again andthe process'would repeat indefinitely, all the relays' sounding like condenser I9. In ther receiving Vcondition it becomes charged,4 and during the momentary opening 'of the contacts it .maintains the current' flow for a sufcient length o'f time for the transfer When the microphone switch 3 is opened, the

to take place.

-circuits return to the receiving condition, and when a conversation has been completed, the

standby condition is restored by restoring the handset to-its cradle. x

The parallel jacks a and 29h are for the purpose of providing operation from' the transmitter-.receiver location in addition to the remote operating position at the call box. Y .It will be understood by those -skilled in the art that our invention isnot restricted .to the exact circuitY arrangement herein shown and described by wayrof illustration. Nor is it'essential that they components of -the system be' combinedV in 'the 7 same manner as illustratively shown.y c

This is overcome bythe use Yof'a large 1. In a two-way communication system, a radio transmitter including modulating means and a source of modulating waves, a radio receiver including a signal responsive device, an antenna common to the transmitter and the receiver, a relay for alternately connecting `the antenna to the input side of the receiver and to the output side of the transmitter, a second relay for connecting a power supply to said transmitter and for causing the attenuation of response Vin said receiver during the operation of said transmitter,

and means including a direct current sourcel 4. A system according to claim 1 and including a transformer for intercoupling Vsaid source fof f modulating waves and said modulating means, said transformer having two primary windings which Vare in circuit with windings kof said relays and with said direct current source.

5. In a two-way communication system, -a radio transmitter, a radio receiver, a hand-set having a microphone for modulating the transmitter-and an earphone for listening to the reception of signals by said receiver, a push button the vcon-.lv

tacts of which are in circuit with said micro*- phone, relay Ymeans operable by said push button Y for conditioning said transmitter` to modulate signalsr as originated at said microphone, an antenna normally connected tothe input sidefof said receiven'and additional relay means in circuit with the first said relay means whereby said vantenna is switched into connection with the output side of said transmitter during talking periods.: Y Y

6. In a two-way radio telephone system,l a transmitter having a power 'supply unit for inter#Y mittent use and a receiver having a power 4supply unit for substantially continuous use, callresponsive means operable upon recep-tion by said receiver of a carrier wave signal initiated at sa remote point, a microphone coupled toa modulator circuit in said transmitter, an earphone coupled to the output circuit of said receiver,

an antenna circuit common to the transmitter and the receiver, relaymeans normally effectiveV to maintain said antenna circuit connected to the input side of said receiver, a transferrelay operable to apply power to said transmitter from its power supply unit, alsoto open thereceiver circuit through said earphone, and an Yoperating circuit for said relay means. and said transfer yrelay comprising fa push button, theimpedance of said microphonarand actuating coils on said relay means and said transfer relay, the circuit last mentioned being effective to condition the system for talking and listeningV at Vmutually exclusiveytimes. i" '7. 'Ina .two-way telephone system, a -trans'- mitter circuit includingV a microphone and a modulator, a receiver "circuit including an fearphone, means "normally connecting the receiver to the e'arphone while maintaining the 'micro-v phone and modulator inoperative, a push-totalk key, relay means controlled by said key and having contacts` for connecting the microphone to the modulator and other contacts whereby the transmitter circuit is conditioned to operate, and means controlled by said relay means for causing a component of the microphone output to be fed to the earphone.

3. In a system according to claim 7, a spark suppressor circuit having series resistance and capacitance in the last said means, said circuit being arranged to be closed by said relay means.

9. In a telephone system a radio receiver hav-- ing means therein for amplifying and rectifying a component of the incoming carrier Wave, a relay operated by said rectied component, a responsive device connected to receive the output from said receiver, and circuit means operative during standby periods for attenuating said output, thereby to suppress noise effects, said circuit means being subject to control by said relay for increasing the signal response level in said responsive device during the reception of a message.

10. In a two-Way communication system, a single antenna for radio transmission and reception, a transmitter having modulating means controllable by a local source of signals, a receiver having responsive means controllable by a remote source of signals, relay means normally set to feed the remote signals from said antenna to said receiver, said relay means being operable to switch the antenna connection from said receiver to said transmitter, an alarm relay operable upon reception of signals from the remote source, an indicator controlled by said alarm relay,

" means for holding said indicator in a standby condition during receipt of said remote signals, said means being manually operable to disconnect the indicator from the receiver during use of said system for two-Way communication, and means independent of the last said means Whereby modulated output signals are caused to be fed from said transmitter to said antenna, said relay means being simultaneously effective to render said receiver unresponsive.

l1. A system according to claim 10 and including means operable simultaneously With said alarm relay for increasing the response level of said receiver to a value above that which is normally maintained during standby periods.

BERTRAM A. TREVOR. JOHN B. ATWOOD.

REFERENCES CITED The following reerences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,165,063 MacKay July 4, 1939 2,223,049 Rechle Nov. 26, 1940 2,206,231 MacKay July 2, 1940 1,857,819 Merriam May 10, 1932 2,289,794 Martin July 14, 1942 2,265,056 Bowers 1 Dec. 2, 1941 1,406,857 Heising Feb. 14, 1922 2,059,870 Holmes Nov. 3, 1936 2,034,565 Dreyer et al. Mar. 17, 1936 2,007,399 Koch July 9, 1935 2,167,058 Van Dyck et al. July 25, 1939 

